Effects of imipramine on raphe nuclei and prefrontal cortex extracellular serotonin levels in the rat.
The effect of acute administrations of three doses of imipramine (1, 5 and 10 mg/kg s.c.), a widely used tricyclic antidepressant, on extracellular levels of serotonin (5-HT) has been studied by intracerebral microdialysis in raphe nuclei and prefrontal cortex of conscious rats. Imipramine 1 mg/kg s.c. did not change extracellular 5-HT in either raphe nuclei and prefrontal cortex. However, with the dose of 5 mg/kg s.c. imipramine induced in raphe nuclei, a brief increase of extracellular 5-HT followed by a lowering (55-65% basal release) of the neurotransmitter. The same dose of imipramine decreased (60-70% of basal value) extracellular 5-HT in prefrontal cortex. Imipramine 10 mg/kg s.c. significantly increased 5-HT levels in both raphe nuclei (190 +/- 20% above basal value) and prefrontal cortex (280 +/- 15% above basal value). Pretreatment with (-)pindolol (5 mg/kg s.c.), a non-selective 5-HT1A subtype receptor antagonist, 30 min before imipramine 5 mg/kg, modified the effect of the antidepressant: an increase, instead of a decrease, on prefrontal cortex dialysate 5-HT was observed. (-)Pindolol (10 mg/kg s.c.) increased extracellular 5-HT in both raphe nuclei (155 +/- 20% above basal value) and prefrontal cortex (160 +/- 8% above basal value). These data show that acute administration of imipramine modifies extracellular 5-HT at the level of the raphe nuclei and prefrontal cortex. 5-HT1A autoreceptors in the raphe nuclei, which this study suggests to be tonically active, may be stimulated after systemic administration of high doses of imipramine.
Maione
S
S
Institute of Pharmacology and Toxicology, Faculty of Medicine and Surgery, 2nd University of Naples, Italy.
Palazzo
E
E
Pallotta
M
M
Leyva
J
J
Berrino
L
L
Rossi
F
F
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D000929:Antidepressive Agents, Tricyclic / Q000494:pharmacology*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D007099:Imipramine / Q000494:pharmacology*; D008297:Male; D017551:Microdialysis; D010869:Pindolol / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000187:drug effects / Q000378:metabolism*; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism*
D000319:Adrenergic beta-Antagonists; D000929:Antidepressive Agents, Tricyclic; D012701:Serotonin; D010869:Pindolol; D007099:Imipramine